1. Field of the Invention
This invention relates to data processing computer system controls and architecture generally and specifically to the so-called "virtual machine" operational systems known as the IBM System 370 and 370/XA and other similar systems.
2. Prior Art
In virtual machine operating systems such as the IBM System 370 or the like, it has long been desirable but not practically feasible to perform temporary suspension of a job running in a particular virtual machine without risking interference with other programs running in other virtual machines in the same system. There are numerous reasons why users of such systems may wish to suspend and ordinarily resume at some later point the work being done as a task in one or more portions of the computer system's workload. A common reason that suspension of a given task or tasks may be requested is to reduce contention for the computer system's resources and to allow temporary allocation of the resources for other work. For example, interactive system users often experience a slower response time when the computer system is occupied with long-term tasks such as batch tasks for which the actual completion time of the task is less critical than those for which the interactive user is contending. In a typical example running the "payroll program" may require several hours of computer system time during which other would-be interactive users experience slow-down or actual inability to access computer resources for their tasks.
Other reasons for halting tasks running in a virtual machine include those of halting the job until some needed resource is available or to suspend the task that is processing until some procedural or processing issue has been resolved.
As noted above, there has not been a practically feasible procedure for performing a suspend and resume operation in a virtual machine running tasks or jobs for users that was not unduly risky or which did not require extreme skill on the part of the operator. Techniques of stopping and restarting processing of a task at acceptable points and in a safe manner not endangering the task or other work on the computer system, may be accomplished, in theory at least, by a skilled system operator. However, it is an extremely delicate and risky procedure that can easily jeopardize all of the work being done in the system. Additionally, these techniques are usually limited to the specific operating system and its current release level of function and may not be conducted in the same system with a given release level different from that for which the techniques have been developed.
Still other approaches require modification of the operating system itself. This is an undesirable situation which most users wish to avoid because of the added risks and maintenance costs associated with creating any error in the operating system which was not produced by the system's original source vendor.
Prior possible techniques for causing a suspend and resume operation in the batch or in a virtual machine processing environment have simply contained unacceptable risk and inconvenience and/or cost and are not suitable for usage by the characteristic users of such a system or of the system operators themselves.
In light of these difficulties with the known prior systems, it is an object of this invention to provide a means of suspending and resuming operation of processing a task in a virtual machine data processing system utilizing only standard available programming and control techniques and without jeopardizing any other programs or processes operating in the data processing system at that time.